Abstract : In an investigation to predict the shielding effectiveness of low-conductivity materials used in electromagneticinterference-shielded structures, the symmetrical configuration of a spherical shell was adapted to approximate the closed walls of a normally cubical or rectangular shielded enclosure. A hemisphere was used for the experiments and a half cube with the same surface area and conductivity (0.1 mho/meter) was used for comparison of an equivalent rectangular structure. In measurements over a frequency range of 20 to 900 Mc (or MHz), the half cube showed a greater shielding effectiveness than the hemisphere over a major portion of the frequency range. The primary advantage of the hemisphere is the ability to predict the absorption over a wide band of frequencies. The conductivity of the materials used in this investigation was found to exhibit an empirical relationship with frequency range, described by log (sigma/sigma sub dc) = 0.236 log f. (Author)